Condition responsive pure fluid oscillator

ABSTRACT

A condition responsive pure fluid oscillator comprising a power nozzle for issuing a power stream, at least one output passage for selectively receiving the power stream, and a hollow control tube aligned generally perpendicular to the power stream flow. Standing waves are produced in the control tube in response to the power stream flowing past the tube mouth. The standing waves produce pressure differentials causing the power stream to oscillate, the frequency of oscillation being adjustable by means of a movable piston within the control tube. The position of the piston in the control tube is made responsive to an external control. The device may serve as a displacement transducer when clearance is provided between the wall of the control tube and the piston, the piston thereby varying the output frequency as a function of its position along the longitudinal axis of the control tube. The oscillator may be employed as a pneumatic eye sensing element whereby the piston is removed and a sensing stream is directed into the control tube from a location external to the oscillator, the oscillator oscillating or not as a function of the presence or absence of the sensing stream at the control tube.

United States Patent [72] Inventor Peter Bauer Germantown, Md. [21]Appl. No. 705,345 [22] Filed Feb. 14, 1968 [45] Patented Jan. 19, 1971[73] Assignee Bowles Engineering Corporation Silver Spring, Md.

a corporation of Maryland [54] CONDITION RESPONSIVE PURE FLUIDOSCILLATOR 17 Claims, 3 Drawing Figs.

[52] US. Cl 137/81.5 [51] Int. Cl.... Fl5c 1/08 [50] Field of Search137/81.5

[56] References Cited UNITED STATES PATENTS 3,185,166 5/1965 Horton eta1 137/81.5 3,204,652 9/1965 Bauer 137/81.5 3,228,410 1/1966 Warren etal. 137/81.5 3,233,522 2/1966 Stern 137/81.5X 3,238,958 3/1966 137/81.53,258,023 6/1966 l37/8l.5 3,273,377 9/1966 Testerman et al.....137/81.5X 3,275,015 9/1966 Meier 137/81.5 4/1968 Kelley et a1. 137/81.5

3,451,269 6/1969 Johnson l37/8l.5X 3,500,850 3/1970 Kelley 137/8 1.53,503,408 3/1970 Metzger. l37/3l.5 3,504,689 4/1970 Lazar 137/8l.5

Primary Examiner-Samuel Scott An0rneyHurvitz, Rose and Greene ABSTRACT:A condition responsive pure fluid oscillator comprising a power nozzlefor issuing a power stream, at least one output passage for selectivelyreceiving the power stream, and a hollow control tube aligned generallyperpendicular to the power stream flow. Standing waves are produced inthe control tube in response to the power stream flowing past the tubemouth. The standing waves produce pressure differentials causing thepower stream to oscillate, the frequency of oscillation being adjustableby means of a movable piston within the control tube. The position ofthe piston in the control tube is made responsive to an externalcontrol. The device may serve as a displacement transducer whenclearance is provided between the wall of the control tube and thepiston, the piston thereby varying the output frequency as a function ofits position along the longitudinal axis of the control tube. Theoscillator may be employed as a pneumatic eye sensing element wherebythe piston is removed and a sensing stream is directed into the controltube from a location external to the oscillator, the oscillatoroscillating or not as a function of the presence or absence of thesensing stream at the control tube.

CONTROL DRlVER on ELEME COHDlTlON stem.

PATENTEUJAM 19m 3556; 120

6 SAGNRL INVEN PETER BQUE 7 1 ER cbmnor ATTORNEY 1 CONDITION RESPONSIVEPURE FLUID OSCILLATOR BACKGROUND OF THE INVENTION The present inventionrelates to fluid oscillators of the organ pipe type and, moreparticularly, to organ pipe oscillators employed as highly sensitivecondition responsive devices.

An organ pipe fluid oscillator operates on the principle that a powerstream may be cyclically deflected by standing waves generated in aresonance tube across the mouth of which the power stream is caused toflow. Such a device is disclosed in U. S, Pat. No. 3,340,884 to R. W.Warren and R. E. Bowles. Oscillators of this type are known to exhibitextremely high frequency stability characteristics over predeterminedpower stream pressure ranges, since the frequency over a given pressurerange is determined almost solely by the effective length of theresonance tube. Consequently organ pipe oscillators are employed inapplications where cyclical fluid pressure signals of stable frequencyare required.

It has been discovered as part of the present invention that, inaddition to serving as highly stable frequency sources, organ pipe fluidoscillators may be modified so as toserve as highly sensitive conditionresponsive devices, such devices having a wide variety of practicalapplications. In one such application, the device may be employed as anaccelerometer, and more specifically, as a highly sensitiveaccelerometer to be employed in space craft travelling beyond theearth's gravitational field. Another application for the controlresponsive organ pipe oscillator relates to extremely sensitive objectdetection and, more particularly, to what are know in the fluidics artas pneumatic eyes."

It is an object of the present invention to provide an organ pipeoscillator sensitive to external conditions.

It is another object of the present invention to provide a displacementtransducer, a speedometer and an accelerometer, each employing a purefluid organ pipe oscillator.

It is still another object of the present invention to provide apneumatic eye employing a condition responsive pure fluid oscillator.

SUMMARY OF THE INVENTION The condition responsive pure fluid organ pipeoscillator of the present invention utilizes a translatable piston inthe resonant or control tube of the organ pipe oscillator, the positionof the piston within the tube being made dependent upon a condition tobe sensed.

Inthe alternative, the oscillations of the organ pipe oscillator may bedestroyed, for instance, by destroying the standing wave patterns in theorgan pipe and thus, provide an on-off or go-no-go type of sensor ofexternal conditions. In employing the organ pipe oscillator as adisplacement transducer in accordance with the principles of the presentinvention, the piston inserted within the resonance tube of theoscillator is of such size as to provide clearance between the innerwalls of the tube and the piston. Displacement of the piston along thelongitudinal axis of the resonant control tube of the oscillatorproduces changes in frequency of the oscillator. The rate of frequencychange is a measure of velocity along the control tube axis.Acceleration may be monitored by providing a spring in the control tubewhich tends to restore the piston to a vertical position. For mostefficient and sensitive operation. the oscillator is designed so thatthe relationship between the orifices of the power nozzle, outputpassage, and resonant control tube are such that there is substantiallyno power stream fluid exhausted through the resonant control tube.

In utilizing the condition responsive organ pipe oscillator as apneumatic eye, a fluid jet is directed toward the open end of theresonant control tube from a location external to the oscillator. Theoscillator can be made to oscillate or not in accordance with the flowor interruption of flow of fluid from the jet into the control tube, theinterruption resulting from detection of an object in the path of thejet.

BRIEF DESCRIPTION OF THE DRAWINGS The above andstill further objects,features and advantages of the present invention will become apparentupon consideration of the following detailed description of severalspecific embodiments thereof, especially when taken in conjunction withthe accompanying drawings, in which:

FIG. I is a partially diagrammatic plan view of a condition responsiveorgan pipe oscillator;

FIG. 2 is a plan view of an organ pipe oscillator employed as adisplacement transducer; and

FIG. 3 is a perspective view of an organ pipe oscillator employed as apneumatic eye.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 of theaccompanying drawings, there is illustrated a pure fluid organ pipeoscillator 10 arranged to provide a variable frequency output signal asa function of a condition or control function to be monitored.Oscillator 10 is typically constructed of two or more laminated sheetsof plastic, metallic, ceramic, or other suitable material. For purposesof illustration, a single sheet is illustrated having the requisitepassages, orifices and grooves defined therein. It is to be understoodthat, where necessary, a top sheet, serving as a fluid seal, is to beplaced over the single sheet to seal the openings and passages describedhereinbelow.

A fluid power source, not illustrated, is connected to a tube 20supplying pressurized fluid to a power nozzle 21. Power nozzle 21 issuesa power stream into a region 23, the left side of which (as viewed inFIG. 1) is open to ambient pressure. The downstream end of region 23 hasa pair of output passages 25 and 27 communicating therewith. Outputpassage 25 is disposed in substantial axial alignment with power nozzle21, output passage 27 is disposed slightly to the left of passage 25 andat a small acute angle with respect thereto. Output passages 25 and 27communicate with a pair of output tubes 29 and 31, respectively, whichin turn may be connected to a fluid sensing and/or utilization device32.

A passage 33, substantially wider than either of the output passages 25and 27 is formed on the right side of power nozzle 21 in region 23 (asviewed in FIG. 1 and communicates with a control tube 35 axially alignedtherewith. The cross-sectional configuration of control tube 35 isillustrated as being circular; however, it is to be understood thatsquare, rectangular, elliptical, or any convenient cross-sectionalconfiguration may be employed. The cross-sectional configuration ofpassage 33 need not be the same as that of tube 35; and in fact, isillustrated as being rectangular in FIG. 1 whereas control tube 35 iscircular. The length of control tube 35 is chosen to provide the minimumdesired frequency for oscillator 10 in accordance with the principles tobe described below. The outer end 36 of tube 35, i.e. the end remotefrom region 23, may either be open to ambient pressure, as illustrated,or closed. If closed, a sufficient opening should be provided in tubeend 36 if necessary to accommodate means for drivinga piston 37 locatedin the tube.

Piston 37, having substantially the same cross-sectional configurationas control tube 35, is disposed within the translatable along the axisof the control tube.

Clearance may be provided or not between the inner wall of control tube35 and the periphery of piston 37. The effect of providing suchclearance is discussed below. The embodiment of FIG. 1 is illustratedwithout substantial clearance between the piston and the tube wall. Theposition of piston 37 within the control tube 35 is determined by anexternally supplied control or condition signal acting through drivermember 39.

Driver member 39 may be any conventional means for displacing a pistonshaft as a function of an input control or condition signal. An exampleof such a device may be found in FIG. 9 of the U. S. Pat No. 3,122,165to B. M. Horton, such device being a pure fluid amplifier which respondsto a differential pressure across its control ports to axially displacea shaft. An electromechanical or electromagnetic driver may be employedto provide electrofluid interfaces or simply a mechanical driver may beemployed to provide a mechanical fluid interface.

The oscillation frequency for oscillator is determined by the effectivelength of control tube 35 which, in turn, is determined by the positionof piston 37. Specifically, as the power stream issues into region 23, adisturbance is created at the mouth of control tube 35 which producesstanding waves in the tube. Since control tube 35 is effectively closedby piston 37, the standing waves are produced in accordance with theclosed tube resonance mode. The alternate condensations and rarefactionstravelling longitudinally in control tube 35 produce cyclical pressuredifferentials across the power stream issued by nozzle 21 so as to causethe power stream to oscillate. The frequency of oscillation isdetermined both by the effective length of tube 35 and the power streampressure. Specifically, the fundamental frequency of closed control pipe35 is equal to the velocity of sound divided by four times the effectivelength of the pipe. As the pressure of the power stream is increasedsuccessively higher harmonics of the fundamental frequency becomedominant to control the oscillation frequency of the power stream. Inaccordance with closed pipe resonance, the first overtone is at threetimes the velocity of sound divided by four times the effective lengthof the control tube, the second overtone is five times the velocity ofsound divided by four times the effective length of the control tube,and the n th overtone is equal to (Zn +1) timesthe velocity of sounddivided by four times the effective length of the control tube.

The unit 10 in FIG. 1 is inherently a monostable device in that thepower stream is normally directed toward output passage 25 and requirescontinued action by a deflecting force in order to be directed towardoutput passage 27. The present invention is not to be deemed limited tomonostable devices, however, since it should be clear to those skilledin the art that other fluidic element configurations may be equallyadapted to operate as organ pipe oscillators. For example, the outputpassages may be disposed symmetrically on either side of the centerlineof power nozzle 21; or the number of output passages may be changed toone, three, etc. sidewalls may be provided in region 23 in order thatthe boundary layer lock-on phenomenon may be utilized to advantage so asto provide monostable or bistable operation; and so on.

The oscillating power stream produces an oscillating pressuredifferential between output tubes 29 and 31. Utilization device 32 maybe a pressure sensitive device responsive to frequency or frequencydifference. Device 32 may either register an indication in terms of thecontrol function or condition being monitored or may alternatively bepart of a closed feedback loop whereby it provides a control signal tomodify the condition which provides the control signal applied to drivermember 39. In addition to the output pressure differential providedacross tubes 29, 31, an acoustic responsive device 40 may be positionedadjacent the left side of region 23 so as to receive the acousticvibrations transmitted by the oscillating power stream. These acousticvibrations may be transduced by device 40 into fluid or electricalsignals as desired. Device 40, like device 32, may be utilized foreither indication or control functions as described. Alternatively, thewalls of the chamber 23 to the left of the centerline of the powernozzle 21 may form an exponential horn to enhance the radiation ofsound.

One possible application for the embodiment of FIG. I is as an outputdevice for a vortex rate sensor. The control signal applied to driverelement 39 may be a fluid pressure differential output signal from avortex rate sensor such as is provided in U. S. Pat. No. 3,320,815, thedifferential pressure being proportional to the angular rate of rotationof the rate sensor. If driver element 39 is then the amplifier of FIG. 9of the above-referenced Horton U.S. Pat. No. 3,122,165, the drive shaftfor piston 37 will be displaced from a neutral position as a function ofthe rotational rate of the vortex rate sensor and the output frequencyat passages 29 and 31 will be a measure of this rotational rate. Byintegrating or differentiating the signal corresponding to angular rate,measures of angular displacement and acceleration respectively may beachieved.

The embodiment of FIG. 1 may also serve as a liquid level sensor.Specifically, where tube 35 is disposed. in a tank of liquid such thatthe liquid level rises in the tube as it rises in the tank, thefrequency of oscillator 10 will change as a function of the liquidlevel. For this application, the liquid level alone without piston 37may be used to vary the oscillator frequency, or piston 37 may beemployed as a float in tube 35.

As mentioned above, for certain applications, it is desirable thatclearance be provided between piston 37 and the inner walls of tube 35.If clearance is so provided, most efficient operation of oscillator 10is achieved where negligible amounts of power stream fluid flow intocontrol tube 35. The relative sizes of the ingress orifices of outputpassages 25 and 27 and the egress orifice of power nozzle 21 may bedesigned to eliminate power stream flow into control tube 35.Specifically, if output passages 25 and 27 are at least equal to orgreater than the width of nozzle 21 or if region 23 is sufficientlyvented to ambient, there is insufficient back pressure produced inregion 23 to cause power stream flow into control tube 35.

An example wherein clearance between the piston and control tube isutilized in the condition responsive organ pipe oscillator of thepresent invention is illustrated in FIG. 2. Oscillator 10, which is thesame as oscillator 10 of FIG. 1, employs piston 37 in control tube 35wherein the piston is somewhat smaller in cross section than the controltube so as to provide clearance, In this way, translation of the piston37 within the control tube 35 is achieved with minimum frictionalengagement therebetween. Of course, if the device in FIG. 2 is operatedin an environment subject to the gravitational field of the earth, therewill be some frictional engagement between the inner wall of tube 35 andthe piston 37' by virtue of the gravitational pull on the piston. Still,however, there will be a translation of piston 37' within the controltube whenever there is movement of the device 10' along the longitudinalaxis of control tube 35. The output frequency is therefore dependentupon the position of piston 37. Operation of the device of FIG. 2 as adisplacement transducer is optimized, of course, in an environment whichis not subject to gravitational forces such as outer space, so thattranslatory motion of piston 37' within tube 35' is substantiallyunaffected by frictional engagement therebetween. End 36' of tube 35should be closed or at least partially restricted to prevent loss ofpiston 37 If necessary or desired, an air-bearing arrangement may beprovided and low force centering springs or magnets may be employed toprovide a zero-acceleration frequen- The operation of the device of FIG.2 with respect to frequency variations is substantially the same as thatfor FIG. 1 described in detail above, the major difference being thatpiston 37' is translated solely by the forces produced upon movement ofdevice 10 longitudinally of tube 35. The output signals produced bydevice 10 in FIG. 2 may be utilized in the same way as discussed abovefor the output signals, both acoustic and fluid, in FIG. 1.

Oscillator 10' may be employed to monitor velocity along the axis ofcontrol tube 35 if the rate of change of the output frequency ismonitored rather than the frequency itself. In addition, oscillator 10may be utilized to monitor acceleration along the axis of control tube35 by employing means for providing a restoring force for piston 37Specifically, a pair of springs secured between piston 37 and respectiveopposite ends of control tube 35 would provide a force tending torestore piston 37' to a neutral position in response to displacement ofthe piston in the control tube, the restoring force being proportionalto the displacement. Calibration of the output signals in terms ofacceleration, velocity or displacement may be achieved by conventionaldifferentiation techniques.

Referring now to FIG. 3, there is illustrated a condition responsiveorganpipe oscillator utilized as a pneumatic eye. Specifically,oscillator is configured substantially the same as oscillator 10 ofFIG. 1. Control tube 35" extends from oscillator 10 in a manner similarto the extension of control tube 35 from oscillator 10 in FIG. 1.Control tube 35" is open at end 36" and has no piston or other memberdisposed therein. A nozzle 41 is disposed in coaxial alignment withcontrol tube 35" and is connected to a suitable source of fluid pressure(not illustrated so as to issue an air stream into end 36" and throughcontrol tube 35". As will be explained in greater detail below, nozzle41 need not be in coaxial alignment with control tube 35" as long as thetwo are positioned so that the air stream from nozzle 41 can disturb thestanding wave pattern in the control tube 35":

The frequency of oscillation of oscillator 10" is determined by thefluid pressure applied to pipe andthe standing wave pattern for an opentube. Specifically, the fundamental frequency of oscillator 10" is equalto the velocity of sound divided by twice the length of tube 35". Thefirst overtone is equal to the velocity of sound divided by the pipelength; the second overtone is equal to three timesthe velocity of sounddivided by two times the pipe length; the n th overtone is equal to (n+1 times the velocity of sound dividedby two times the pipe length. Thepredominant overtone is determined by the pressure .at tube 20, thegreater the pressure the higher the overtone. Once oscillator 10" is.set for operation at a predetermined frequency, the pressure of thecontrol stream issuing from nozzle 41 may be made sufficiently great asto overcome the effects of standing waves generated in control tube 35",ineffect reducing the effective length of tube 35" to zero. When thecontrol strearnis receivedby tube 35", the standing-wave patterns in thetube are destroyed and the oscillations cease. It may be readily seen,therefore, that oscillator 10", in conjunction with the jet issuing fromnozzle 41, comprises a pneumatic eye which detects the presence of anobject between nozzle 41 andcontrol tube 35.; the oscillator is enabledwhen a detected object is in blocking relationship between the nozzle 41and tube 35" and is inhibited when the control stream from nozzle 41 isnot blocked.

The pneumatic'eye of FIG. 3 may be made substantially more sensitive todetectedobjects than prior art, pneumatic eyes, such as the pneumaticeye disclosed in U. S. Pat. No.

3,258,023 to R. EQBowles. In the Bowles pneumatic eye, a monostablefluidic device normally issues a power stream from a first of two outputpassages. A detection stream is at the outlet end of the first of saidoutlet passages and, when not blocked, back loads the passage to' switchthe power stream to the second output passage. The pressure of thedetection stream must be sufficiently great to back load the first ofsaid outlet passages. The pressure of applicants detection stream neednot be nearly so great however because oscillator 10" can be adjusted torespond to even a slight disturbance in control tube 35". The extremesensitivity of applicant's pneumatic eye is made possible by the'factthat the organ pipe oscillator 10" is capable of operating at discretefrequencies, namely the fundamental and various overtones thereof.Specifically, for a given range of power stream pressures, thefundamental frequency will be dominant to control oscillation of thepower stream. At a higher range of input pressures the first overtonedominates, at a still higher range of input pressures the secondovertone dominates, and so on. A very small, but critical range ofpressures exists between each of the above-defined pressure ranges, thepressure in these critical ranges being such that the power stream isrendered nonoscillatory. 1f the power stream pressure is set at one ofthese critical ranges between oscillatory modes for oscillator 10'',merely the slightest disturbance in control tube 35 renders the powerstream oscillatory.

Employing the above principles, a pneumatic eye can be provided in whichthe oscillator is made to oscillate in the absence of an object and isrendered nonoscillatory in the presence of an object. The pressure ofthe power stream in oscillator 10'' is set within one of the aforesaidcritical ranges, and the pressure of the control jet issuing from nozzle41 is made just great enough to produce a slight disturbance in-controltube 35 sufficient to upset the delicate pressure balance in region 23and initiate oscillationin oscillator 10". When a detected object isdisposed to block the jet from nozzle 41, the oscillations cease.Similarly, if it is desired to provide pneumatic eye operation in whichoscillation signifies a detected object, the power stream pressure canbe set just outside of one of the critical pressure ranges so thatreceipt of the low pressure detection stream at control tube 35"inhibits oscillation. When a detected object blocks the detectionstream. the

oscillations resume to signify detection.

In either of the above operational modes, detection is extremelysensitive. ln fact, organ pipe oscillator 10" has been found to respond(i.e. change from oscillatory to nonoscillatory modes and vice versa) toacoustic disturbances received by control tube 35" independently of thedetection stream issued by nozzle 4l. Thus a prowler detector isprovided.

While the pneumatic eye of FIG. 3 as thus far described provides atemporary indication (oscillation or nonoscillation) in response to adisturbance in control tube 35', the pneumatic eye may also be operatedso as to have a memory feature; that is, the condition (oscillation ornonoscillation) to which oscillator 10" is switched in response to adisturbance may be retained after the disturbance ceases. The memoryfeature is achieved by setting the power stream pressure sufficientlyclose to a boundary pressure in one of the above-described criticalpressure ranges. Thus, by setting the power stream pressure within andat the very end of a critical range, a disturbance willproduceoscillation that is maintained even after the disturbance is removed.Similarly, setting the power stream pressure just outside one of thesecritical pressure ranges results in oscillations being inhibited inresponse to a disturbance and remaining inhibited after the disturbanceceases. The reason for the memory capability of oscillator 10" when thepower stream pressure is set as stipulated is a hysteresis effect in thefrequency versus power stream pressure characteristic of the unit.

In still another pneumatic eye embodiment of the present inventionutilization is made of a second control nozzle 43 which issues a secondcontrol stream in interacting relationship with the control streamissued from control nozzle 41. The nozzles are arranged so that theobject to be detected passes through the path of the stream issuing fromcontrol nozzle 43, and the detection of such an object may eitherproduce or inhibit oscillation in oscillator 10'. Thus oscillator 10 maybe biased as described above to oscillate when no stream is received intube 35 the stream issued from control nozzle 43 normally deflecting thestream issued from control nozzle 41 away from control tube 35".Oscillator 10 continues to oscillate until such time as an object isdetected in the path of the stream issuing from control nozzle 43. Thisprevents deflection of the stream issuing from control nozzle 41, whichstream thereby enters control tube 35" at a sufficientpressure level todestroy the standing wave patterns therein and inhibit oscillation.

Conversely the pressure level of the powerstream can be set inaccordance with the critical pressure ranges discussed to provide anoscillatory signal .from oscillator 10' only when an object is detectedin front of nozzle 43, the oscillations being otherwise inhibited.Likewise, the memory feature discussed above may be employed byutilizing biasing techniques discussed above.

In a particular embodiment of the pneumatic eye built and tested,excellent results were achieved with a distance between control tube 35"and control 'nozzle 41 of 1 foot and a distance from control nozzle 43to the jet issued from control nozzle 41 of 3 feet. Of course, larger orsmaller distances are possible, these being employed as a function ofthe pressure levels utilized.

From the above description, it should be apparent that the stream issuedfrom nozzle 41 need not be directed axially into tube 35". Specifically,the stream may be directed in any manner which causes a disturbancesufficient to alter the standing wave patterns in the tube.

In addition to the above-described embodiment, numerous otherapplications of the condition responsive organ pipe oscillator describedherein may come to mind from the above disclosure. Specifically, logicelements such as NOR, AND, OR and NAND gates may be constructed wherebyan oscillatory output signal is produced or not as a function of thevarious input signals which direct or deflect the control stream fromnozzle 41 relative to control tube 35" of FIG. 3 as a function of thelogic desired. The advantage of such an application is the high gainoutput signal produced in the form of the oscillating power streamsignal received by passages 29 and 31.

Of course, the precise configuration of oscillator of P10.

1 should not be construed as limiting. For example, the oscillator mayhave opposed control tubes such as the oscillator described in U. 5.Pat. No. 3,340,884 to R. W. Warren and R. E. Bowles rather than a singlecontrol tube as illustrated herein. Further, the region 23 may beconstructed such that the open area to the left of the power stream, asviewed in FIG. 1, is closed off by a sidewall which would render thepower stream bistable. More specifically, the power stream would lock-onto one or both sidewalls, to be displaced only by a force sufficient toovercome lock-on provided against the power stream.

While I have described and illustrated one specific embodiment of myinvention, it will be clear that variation of the details ofconstruction which are specifically illustrated and described may beresorted to without departing from the spirit and scope of the inventionas defined in the appended claims.

I claim:

1. A condition responsive oscillator comprising:

a pure fluid amplifier having a power nozzle responsive to pressurizedfluid applied thereto for issuing a power stream, at least one outputpassage for selectively receiving said power stream, and means fordeveloping cyclically varying pressure diflerentials across said powerstream, said means comprising at least one control tube having apredetermined length and having one end located adjacent the powerstream such that power stream flow thereby produces a disturbance in thecontrol tube resulting in the generation of standing waves therein, thelength of said standing waves being determined by the length of saidcontrol tube, whereby the power stream is cyclically deflected relativeto said output passage at a frequency determined by the length of saidcontrol tube; and

control means responsive to said condition for varying the effectivelength of said standing waves as a function of said condition.

2. The combination according to claim I wherein said control meanscomprises a piston member disposed within said control tube andtranslatable axially therealong as a function of said condition to varythe effective length of said control tube.

3. The combination according to claim 2 wherein said means fortranslating comprises a shaft secured to said piston member and meansfor translating said shaft axially along said control tube as a functionof said condition.

4. The combination according to claim 2 wherein said control tube isclosed at its end remote from the power stream, said piston member beingtranslatable in said control tube as a function of translation of saidcontrol tube along it axis.

5. The combination according to claim 4 wherein sufficient clearance isprovided between said piston member and the interior of said controltube as to render friction therebetween negligible.

6. The combination according to claim 4 further comprising means forproviding a restoring force to said piston member in response totranslation thereof in said control tube, said restoring force beingproportional to the displacement of said piston from a predeterminedposition relative to said control tube.

7. The combination according to claim 1 wherein said control meansincludes a control nozzle for producing a flowing fluid stream directedagainst the end of said control tube remote from said power stream, saidpower stream being rendered oscillatory and nonoscillatory in accordancewith the presence and absence of said flowing-fluid stream in saidcontrol tube. Y

8. The combination according to claim 7'wherein the pressure of saidpressurized fluid applied to saidpower nozzle is such that said powerstream is rendered oscillatory by said standing waves in the absence ofsaid flowing fluid stream in said control tube, and wherein the pressureof said flowing fluid stream is sufficient to render said power streamnonoscillatory when received in said control tube.

9. The combination according to claim 8 wherein is further provided afurther control nozzle for issuing a further fluid. stream whichdeflects said flowing fluid stream, whereby interruption of said furtherfluid stream permits reception of said flowing fluid stream in saidcontrol tube to inhibit oscillation of said power stream.

10. The combination according to claim 7 wherein the pressure of saidpressurized fluid applied to said power nozzle is such that said powerstream is rendered nonoscillatory in the absence of any disturbance ofsaid control tube, and wherein the pressure of said flowing fluid streamis sufficient to initiate oscillation of said power stream when receivedby said control tube.

11. The combination according to claim 10 wherein the pressure of saidpressurized fluid applied to said power nozzle is such that said powerstream is rendered nonoscillatory in the absence of any disturbance ofsaid control tube, and wherein the pressure of said flowing fluid streamis sufficient to initiate oscillation of said power stream when receivedby said control tube.

12. The condition responsive oscillator according to claim 1 furthercomprising utilization means responsive to the frequency of deflectionof said power stream.

13. The condition responsive oscillator according to claim 12 whereinsaid utilization means is a pressure sensitive device connected to saidoutput passage.

14. The condition responsive oscillator according to claim 1 whereinsaid pure fluid amplifier includes an interaction region with which saidpower nozzle, output passage and control tube communicate and into whichsaid power stream is issued generally toward said output passage, saidone end of said control tube being disposed at one side of saidinteraction region, the opposite side of said interaction region beingopen to ambient pressure.

15. The condition responsive oscillator according to claim 14 whereinsaid opposite side of said interaction region is so configured toconduct acoustic vibrations transmitted by the cyclically deflectedpower stream, and further comprising transducer means for convertingacoustic vibrations so conducted into signals.

16. A condition responsive oscillator comprising:

a fluidic element having a power nozzle responsive to pressurized fluidapplied thereto for issuing a power stream, at least one output passagefor selectively receiving said power stream, and means for developingcyclically varying pressure differentials across said power stream, saidmeans comprising at least one control tube containing a column ofambient fluid and having an open end located. adjacent the power streamsuch that the power stream flow thereby disturbs the ambient fluid insaid control tube resulting in the generation of standing waves therein,the length of said standing waves being determined by the length of said.column of ambient fluid, said standing waves cyclically deflecting saidpower stream at a frequency determined by the length of said column ofambient fluid in said control tube; and

control means comprises a piston member disposed within said controltube and translatable axially therealong as a function of saidcondition.

1. A condition responsive oscillator comprising: a pure fluid amplifierhaving a power nozzle responsive to pressurized fluid applied theretofor issuing a power stream, at least one output passage for selectivelyreceiving said power stream, and means for developing cyclically varyingpressure differentials across said power stream, said means comprisingat least one control tube having a predetermined length and having oneend located adjacent the power stream such that power stream flowthereby produces a disturbance in the control tube resulting in thegeneration of standing waves therein, the length of said standing wavesbeing determined by the length of said control tube, whereby the powerstream is cyclically deflected relative to said output passage at afrequency determined by the length of said control tube; and controlmeans responsive to said condition for varying the effective length ofsaid standing waves as a function of said condition.
 2. The combinationaccording to claim 1 wherein said control means comprises a pistonmember disposed within said control tube and translatable axiallytherealong as a function of said condition to vary the effective lengthof said control tube.
 3. The combination according to claim 2 whereinsaid means for translating comprises a shaft secured to said pistonmember and means for translating said shaft axially along said controltube as a function of said condition.
 4. The combination according toclaim 2 wherein said control tube is closed at its end remote from thepower stream, said piston member being translatable in said control tubeas a function of translation of said control tube along it axis.
 5. Thecombination according to claim 4 wherein sufficient clearance isprovided between said piston member and the interior of said controltube as to render friction therebetween negligible.
 6. The combinationaccording to claim 4 further comprising means for providing a restoringforce to said piston member in response to translation thereof in saidcontrol tube, said restoring force being proportional to thedisplacement of said piston from a predetermined position relative tosaid control tube.
 7. The combination according to claim 1 wherein saidcontrol means includes a control noZzle for producing a flowing fluidstream directed against the end of said control tube remote from saidpower stream, said power stream being rendered oscillatory andnonoscillatory in accordance with the presence and absence of saidflowing fluid stream in said control tube.
 8. The combination accordingto claim 7 wherein the pressure of said pressurized fluid applied tosaid power nozzle is such that said power stream is rendered oscillatoryby said standing waves in the absence of said flowing fluid stream insaid control tube, and wherein the pressure of said flowing fluid streamis sufficient to render said power stream nonoscillatory when receivedin said control tube.
 9. The combination according to claim 8 wherein isfurther provided a further control nozzle for issuing a further fluidstream which deflects said flowing fluid stream, whereby interruption ofsaid further fluid stream permits reception of said flowing fluid streamin said control tube to inhibit oscillation of said power stream. 10.The combination according to claim 7 wherein the pressure of saidpressurized fluid applied to said power nozzle is such that said powerstream is rendered nonoscillatory in the absence of any disturbance ofsaid control tube, and wherein the pressure of said flowing fluid streamis sufficient to initiate oscillation of said power stream when receivedby said control tube.
 11. The combination according to claim 10 whereinthe pressure of said pressurized fluid applied to said power nozzle issuch that said power stream is rendered nonoscillatory in the absence ofany disturbance of said control tube, and wherein the pressure of saidflowing fluid stream is sufficient to initiate oscillation of said powerstream when received by said control tube.
 12. The condition responsiveoscillator according to claim 1 further comprising utilization meansresponsive to the frequency of deflection of said power stream.
 13. Thecondition responsive oscillator according to claim 12 wherein saidutilization means is a pressure sensitive device connected to saidoutput passage.
 14. The condition responsive oscillator according toclaim 1 wherein said pure fluid amplifier includes an interaction regionwith which said power nozzle, output passage and control tubecommunicate and into which said power stream is issued generally towardsaid output passage, said one end of said control tube being disposed atone side of said interaction region, the opposite side of saidinteraction region being open to ambient pressure.
 15. The conditionresponsive oscillator according to claim 14 wherein said opposite sideof said interaction region is so configured to conduct acousticvibrations transmitted by the cyclically deflected power stream, andfurther comprising transducer means for converting acoustic vibrationsso conducted into signals.
 16. A condition responsive oscillatorcomprising: a fluidic element having a power nozzle responsive topressurized fluid applied thereto for issuing a power stream, at leastone output passage for selectively receiving said power stream, andmeans for developing cyclically varying pressure differentials acrosssaid power stream, said means comprising at least one control tubecontaining a column of ambient fluid and having an open end locatedadjacent the power stream such that the power stream flow therebydisturbs the ambient fluid in said control tube resulting in thegeneration of standing waves therein, the length of said standing wavesbeing determined by the length of said column of ambient fluid, saidstanding waves cyclically deflecting said power stream at a frequencydetermined by the length of said column of ambient fluid in said controltube; and control means responsive to said condition for varying thelength of said column of ambient fluid in said control tube as afunction of said condition.
 17. The combination according to claim 16wherein said control means comprises a piston member disposed withinsaid coNtrol tube and translatable axially therealong as a function ofsaid condition.